Pluhlese..VNC with VPN help needed

I'm in IT and work with Windows machines all day, so of course I use a Mac at home. I can't use VNC over VPN (PPTP) on my Mac (10.3.9). Here's what I've figured out works and doesn't work:

What doesn't work:
Various Mac VNC programs (chicken of vnc, vncthing, vncdimension)
MS Remote Desktop for Mac
Company Intranet web sites

What does work:
VNC over VPN on my home PC (Win XPsp2)
Connecting to company network shares with Finder
VNC connecting to my home PC
Getting exchange email via Mail program on the Mac

I'm using 192 IP's at home and internally at work. I think it has something to do with what port numbers I'm using on my Mac, but I can't get it figured out. I've done way too much googling, hair pulling and cussing to be healthy, so I come now asking for your help.